Synthesis of multi-cavity mesoporous carbon nanospheres through solvent-induced self-assembly: Anode material for sodium-ion batteries with long-term cycle stability

Mesoporous carbon nanospheres (MCSs) are extensively employed in energy storage applications due to their ordered pore size, large specific surface area (SSA), and abundant active sites, resulting in excellent electrochemical performance for sodium storage. However, challenges persist in achieving precise structural control and stable synthesis reactions for these MCSs. Additionally, employing MCSs with a larger SSA in sodium storage applications can lead to increased side reactions and potential structural instability. To address these issues, we propose a solvent-induced self-assembly method for obtaining high nitrogen-containing multi-cavity MCSs with reduced SSA. The morphology and SSA of the nanospheres can be precisely adjusted by regulating the reaction time. Introducing an amine-phenol bridging structure into the polymer system significantly bolsters the structural and morphological stability of the mesoporous materials. The performance of these novel nanospheres in sodium-ion batteries (SIBs) is remarkable, exhibiting excellent sodium storage capability and exceptional ultra-long cycle stability. At a rate of 0.1 A g-1, the nanospheres achieved a high reversible capacity of 252 mAh g-1, and even after 20,000 cycles at 5 A g-1, a specific capacity of 136 mAh g-1 was retained. In summary, our study presents a novel approach for synthesizing mesoporous carbon materials and offers valuable insights for sodium storage research, opening new possibilities for enhancing energy storage applications.

Tailoring diamondised nanocarbon-loaded poly(lactic acid) composites for highly electroactive surfaces: extrusion and characterisation of filaments for improved 3D-printed surfaces

A new 3D-printable composite has been developed dedicated to electroanalytical applications. Two types of diamondised nanocarbons - detonation nanodiamonds (DNDs) and boron-doped carbon nanowalls (BCNWs) - were added as fillers in poly(lactic acid) (PLA)-based composites to extrude 3D filaments. Carbon black served as a primary filler to reach high composite conductivity at low diamondised nanocarbon concentrations (0.01 to 0.2 S/cm, depending on the type and amount of filler). The aim was to thoroughly describe and understand the interactions between the composite components and how they affect the rheological, mechanical and thermal properties, and electrochemical characteristics of filaments and material extrusion printouts. The electrocatalytic properties of composite-based electrodes, fabricated with a simple 3D pen, were evaluated using multiple electrochemical techniques (cyclic and differential pulse voltammetry and electrochemical impedance spectroscopy). The results showed that the addition of 5 wt% of any of the diamond-rich nanocarbons fillers significantly enhanced the redox process kinetics, leading to lower redox activation overpotentials compared with carbon black-loaded PLA. The detection of dopamine was successfully achieved through fabricated composite electrodes, exhibiting lower limits of detection (0.12 μM for DND and 0.18 μM for BCNW) compared with the reference CB-PLA electrodes (0.48 μM). The thermogravimetric results demonstrated that both DND and BCNW powders can accelerate thermal degradation. The presence of diamondised nanocarbons, regardless of their type, resulted in a decrease in the decomposition temperature of the composite. The study provides insight into the interactions between composite components and their impact on the electrochemical properties of 3D-printed surfaces, suggesting electroanalytic potential.

N-Doped sp2 /sp3 Carbon Derived from Carbon Dots to Boost the Performance of Ruthenium for Efficient Hydrogen Evolution Reaction

The structure and properties of the carrier significantly affect the catalytic activity of the active centers for supported electrocatalysts. Therefore, elaborate design and regulation of the physicochemical properties of carbon carriers are essential to improve the activity and stability of the carbon-supported ruthenium-based catalysts. Herein, enlightened by the unique characteristics of coexisting sp² and sp³ carbon nuclei in N-doped carbon dots (NCDs), a hybrid structure of N-doped carbon substrates featuring N-doped sp² /sp³ carbon interfaces loaded with Ru nanoparticles (Ru/NCDs) is obtained. Spectroscopic analysis and density functional theory calculations illustrate that the interaction between Ru and NCDs effectively modulates the electronic structure of the active center Ru, and the formed N-doped sp² /sp³ carbon interface lowers the energy barrier of the intermediates in hydrogen evolution reaction (HER) and balances the hydrogen adsorption and desorption and, thereby, greatly improves the activity of Ru/NCDs. Remarkably, Ru/NCDs exhibit excellent HER activity and stability in comparison to Pt/C, which merely requires overpotentials as low as 37 and 14 mV at 10 mA cm^-2 in alkaline and acidic electrolytes, respectively. This finding will provide more thoughts about the influence of substrate properties on the catalytic activity and rational design of carbon-loaded electrocatalysts.

Atomically dispersed metal catalysts on nanodiamond and its derivatives: synthesis and catalytic application

Atomically dispersed metal catalysts (ADMCs) have attracted increasing interest in the field of heterogeneous catalysis. As sub-nanometric catalysts, ADMCs have exhibited remarkable catalytic performance in many reactions. ADMCs are classified into two categories: single atom catalysts (SACs) and atomically dispersed clusters with a few atoms. To stabilize the highly active ADMCs, nanodiamond (ND) and its derivatives (NDDs) are promising supports. In this Feature Article, we have introduced the advantages of NDDs with a highly curved surface and tunable surface properties. The controllable defective sites and oxygen functional groups are known as the anchoring sites for ADMCs. Tunable surface acid-base properties enable ADMCs supported on NDDs to exhibit unique selectivity towards target products and an extended lifetime in many reactions. In addition, we have firstly overviewed the recent advances in the synthesis strategies for effectively fabricating ADMCs on NDDs, and further discussed how to achieve the atomic dispersion of metal precursors and stabilize the as-formed metal atoms against migration and agglomeration based on NDDs. And then, we have also systematically summarized the advantages of ADMCs supported on NDDs in reactions, including hydrogenation, dehydrogenation, aerobic oxidation and electrochemical reaction. These reactions can also effectively guide the design of ADMCs. The recent progress in understanding the effect of structure of active centers and metal-support interactions (MSIs) on the catalytic performance of ADMCs is particularly highlighted. At last, the possible research directions in ADMCs are forecasted.

Untangling Cooperative Effects of Pyridinic and Graphitic Nitrogen Sites at Metal-Free N-Doped Carbon Electrocatalysts for the Oxygen Reduction Reaction

Metal-free carbon electrodes with well-defined composition and smooth topography are prepared via sputter deposition followed by thermal treatment with inert and reactive gases. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy show that three carbons of similar N/C content that differ in N-site composition are thus prepared: an electrode consisting of almost exclusively graphitic-N (N_G ), an electrode with predominantly pyridinic-N (N_P ), and one with ≈1:1 N_G :N_P composition. These materials are used as model systems to investigate the activity of N-doped carbons in the oxygen reduction reaction (ORR) using voltammetry. Results show that selectivity toward 4e-reduction of O₂ is strongly influenced by the N_G /N_P site composition, with the material possessing nearly uniform N_G /N_P composition being the only one yielding a 4e-reduction. Computational studies on model graphene clusters are carried out to elucidate the effect of N-site homogeneity on the reaction pathway. Calculations show that for pure N_G -doping or N_P -doping of model graphene clusters, adsorption of hydroperoxide and hydroperoxyl radical intermediates, respectively, is weak, thus favoring desorption prior to complete 4e-reduction to hydroxide. Clusters with mixed N_G /N_P sites display synergistic effects, suggesting that co-presence of these sites improves activity and selectivity by achieving high theoretical reduction potentials while facilitating retention of intermediates.

Construction of a sp3 /sp2 Carbon Interface in 3D N-Doped Nanocarbons for the Oxygen Reduction Reaction

The development of highly efficient metal-free carbon electrocatalysts for the oxygen reduction reaction (ORR) is one very promising strategy for the exploitation and commercialization of renewable and clean energy, but this still remains a significant challenge. Herein, we demonstrate a facile approach to prepare three-dimensional (3D) N-doped carbon with a sp³ /sp² carbon interface derived from ionic liquids via a simple pyrolysis process. The tunable hybrid sp³ and sp² carbon composition and pore structures stem from the transformation of ionic liquids to polymerized organics and introduction of a Co metal salt. Through tuning both composition and pores, the 3D N-doped nanocarbon with a high sp³ /sp² carbon ratio on the surface exhibits a superior electrocatalytic performance for the ORR compared to that of the commercial Pt/C in Zn-air batteries. Density functional theory calculations suggest that the improved ORR performance can be ascribed to the existence of N dopants at the sp³ /sp² carbon interface, which can lower the theoretical overpotential of the ORR.

Vertically Aligned N-Doped Diamond/Graphite Hybrid Nanosheets Epitaxially Grown on B-Doped Diamond Films as Electrocatalysts for Oxygen Reduction Reaction in an Alkaline Medium

Diamond/graphite hybrid nanosheets (DGNSs) have been epitaxially grown on boron-doped diamond (BDD) films from CH₄/H₂ mixture gas by microwave plasma chemical vapor deposition. The DGNSs are vertically aligned on the crystal facets of the BDD films uniformly, densely, and orderly. The DGNSs are composed of the core diamond sheets and the surface graphitic overlayers, which possess an open edge structure. By posttreatment in NH₃ atmosphere in a microwave plasma or a tube furnace, the N-doped DGNSs (NDGNSs) were obtained. The electrocatalytic performance toward oxygen reduction reaction (ORR) for the DGNSs was greatly enhanced after doping with N, and the doped pyridinic N contributes more to the ORR. The electrocatalytic activity for ORR of the NDGNSs doped at 650 °C in NH₃ in a tube furnace is the highest in all of the samples, which is comparable to the commercial Pt/C. The present work provides a novel electrocatalyst for the ORR with high performance.

Catalysis by hybrid sp2/sp3nanodiamonds and their role in the design of advanced nanocarbon materials

Hybrid sp²/sp³nanocarbons, in particular sp³-hybridized ultra-dispersed nanodiamonds and derivative materials, such as the sp³/sp²-hybridized bucky nanodiamonds and sp²-hybridized onion-like carbons, represent a rather interesting class of catalysts still under consideration.

Carbon nano-onions: large-scale preparation, functionalization and their application as anode material for rechargeable lithium ion batteries

Carbon nano-onions (CNOs) are one of the most promising anode materials for lithium ion batteries (LIBs) because of their outstanding physicochemical properties.

Order of Activity of Nitrogen, Iron Oxide, and FeNx Complexes towards Oxygen Reduction in Alkaline Medium

In alkaline medium, it seems that both metal-free and iron-containing carbon-based catalysts, such as nitrogen-doped nanocarbon materials, FeOx -doped carbon, and Fe/N/C catalysts, are active for the oxygen reduction reaction (ORR). However, the order of activity of these different active compositions has not been clearly determined. Herein, we synthesized nitrogen-doped carbon black (NCB), Fe3 O4 /CB, Fe3 O4 /NCB, and FeN4 /CB. Through the systematic study of the ORR catalytic activity of these four catalysts in alkaline solution, we confirmed the difference in the catalytic activity and catalytic mechanism for nitrogen, iron oxides, and Fe-N complexes, respectively. In metal-free NCB, nitrogen can improve the ORR catalytic activity with a four-electron pathway. Fe3 O4 /CB catalyst did not exhibit improved activity over that of NCB owing to the poor conductivity and spinel structure of Fe3 O4 . However, FeN4 coordination compounds as the active sites showed excellent ORR catalytic activity.